1. Field of the Invention
The present invention relates generally to a parts mounting inspection apparatus, an inspection apparatus thereof and a board inspected by the same apparatus and, more particularly, to a technology of automatically inspecting existence or non-existence and mounting states of respective parts mounted on a printed circuit board or a hybrid IC.
2. Related Background Art
A trigonometrical measuring method based on a light spot method and a light cutting method as an applied method thereof have hitherto been often utilized for automatically checking mounting states of electronic parts mounted on the printed circuit board or the hybrid IC.
An explanation for the prior art will be given with reference to the drawings. FIG. 12 is a diagram showing a measurement principle of the trigonometrical measuring method based on the conventional light spot method. As illustrated in FIG. 12, a convergent laser beam 18 is incident vertically on a part 15 mounted on a printed circuit board 6 from a laser output unit (LD) 2 to form a spot on the part 15.
This spot beam in turn forms an image on a PSD 17 after being transmitted through an image forming optical system 16. Based on the trigonometrical measuring principle, the height of the part 15 in a predetermined position is determined. Such a measuring operation is repeated a predetermined number of times by relatively scanning the printed circuit board with the laser beams, thereby inspecting the existence or non-existence and a mounting posture of the part 15 on the printed circuit board 6.
In the above-mentioned conventional example, however, the following problems arise, because it is based on the trigonometrical measuring method. To be specific, referring to FIG. 12, i.e., the diagram of assistance in explaining the principle of the trigonometrical measuring method:
(1) The PSD sensor 17 and an incidence optical axis 18 must have a predetermined angle or greater, and hence there are constraints in terms of mounting intervals of the parts and heights because of the impossibility of avoiding a dead angle caused especially by a taller part 19 provided in the vicinity of the part 15:
(2) A measuring circuit automatically judges the center of the spot beam or the maximum reflecting position as a spot irradiating position, and it is, therefore, impossible to perform a precise check because of an error in the measurement value if a density difference exists due to an existence of a print display unit within the spot beam range: and
(3) The PSD sensor 17 and the incidence optical axis 18 must have the predetermined angle or greater, and hence the distances between the part 15 to be checked, the sensor 17 and the optical system have to be made close to some extent.